Experiment: John L. Fitzpatrick and his colleagues conducted an experiment regarding sperm competition through an examination of the sperm characteristics of 29 closely related cichlid species from Lake Tanganyika. This experiment is conducted to test and/or verify the sperm competition theory that sperm traits determined fertilization success. Reproductively active males are collected and analyzed. Sperm number, lengths, longevity and swimming speeds were measured. The researchers also used phylogenetic analyses to reconstruct the probable evolutionary route of sperm trait evolution in cichlids that leads to the evolution of faster sperm.
Relationship between sperm speed and sperm size Results: With the use of phylogenetic analyses, the impacts of sperm competition to sperm traits were assessed. The directional test of trait evolution shows that within the 29 species of cichlids in Tanganyika Lake, large and fast sperm evolved from small and slow sperm in response to increases in the strength of sperm competition. Conclusion: The experiment supports the sperm competition theory by showing a positive correlation between sperm length and swimming speed exist.
The experiment showed how female mating behavior may have acted to shape the various sperm traits and to produce superior sperms. This study highlights the selective pressures that trigger evolution in sperm traits. Source: J. L. Fitzpatricka, R. Montgomeriec, J. K. Desjardinsb, K. A. Stiverb, N. Kolmf, and S. Balshineb. Female promiscuity promotes the evolution of faster. PNAS Vol. 106 No. 4 (2009) What If? What experimental results would you predict regarding the sperm traits if female cichlids are not promiscuous?
Justification: First year biology textbooks try to give its readers a brief overview about higher biology concepts and data. Since its main purpose is to introduce the field of biology to the student, technical information is not thoroughly discussed. It is important that examples reflect something that is easy to understand. Biology is an umbrella term that encompassed other specific but related fields. The experiment by Fitzpatrick and colleagues discussed the concepts that range between the field of ecology and evolution.
Simply speaking, it falls under evolutionary ecology. As an introduction to the specific fields under biology, the experiment interestingly showed how evolution affects the species of cichlids through female sexual behavior that promotes selection in the sperm traits. It discussed evolution in terms of selection of traits in terms of physical attributes rather than expressing the process through complicated concepts such as genes and gene pools. Thus, the text box is interesting, encompassing yet easy to understand.
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